1. Field of the Invention
The present invention relates to a developing material amount detecting apparatus for use in an electrographic copying machine.
2. Description of the Prior Art
Generally, in an electrographic copying machine, the developing material, particularly toner is consumed each time the copying operation is carried out. Thus, it is necessary to supply toner into the developing apparatus from the supply tank at an amount equal to the amount consumed for developing, and also, it is necessary to load the supply tank with toner when the amount of toner contained in the supply tank becomes small. To this supplying and loading, it is necessary to detect the amount of developing material contained in the developing tank of the developing apparatus and/or in the supply tank.
According to the prior art, the detection of the amount of developing material is done by a pressure sensor or magnetic sensor provided in the wall of the tank. However, such a sensor is expensive, and the detection by such a sensor has low stability and low reliability.
An improved apparatus for detecting the amount developing material has been proposed, such as disclosed in U.S. Pat. No. 4,277,003 issued July 7, 1981 to Tabuchi et al. According to this reference, a stirring member is provided movably inside the tank and it is forced to moved intermittently against a force by a biasing means. The developing material amount detecting apparatus disclosed in this reference generates a signal representing the amount of decrease of the developing material in response to a position at which the stirring member returns upon removal of the force.
The above described developing material amount detecting apparatus is based on the fact that the returning of the stirring member by the biasing means is restricted by the developing material contained in the tank, whereby the returned position of the stirring member indicates the amount of the developing material remaining in the tank. Since the returned position of the stirring member can be detected using microswitches or the like, the detection which is based on the on and off operation of the microswitch is very stable and, yet, the detecting apparatus can be manufactured at low cost when compared with the prior art detecting apparatus employing the pressure sensor or magnetic sensor. However, according to the above described detecting apparatus, since the remaining amount of the developing material is detected merely by the returned position of the stirring member, the detected amount is not very precise and, therefore, the problem still exists in the reliability. Furthermore, the detected amount depends on the size and configuration of the stirring member and also on the strength of the biasing means, the relationship between the returned position of the stirring means and the amount of remaining developing material in the tank is not necessarily the same among a number of developing material amount detecting apparatuses. Therefore, precise adjustments are needed in each developing material amount detecting apparatus by changing the various settings in trial and error attempts, resulting in a time consuming and difficult task.